Fuel cells and electrolyzer cells are generally referred to as electrochemical cells. Fuel cells have been proposed as clean, efficient and environmentally friendly power sources that have various applications. A conventional proton exchange membrane (PEM) fuel cell is typically comprised of an anode, a cathode, and a selective electrolytic membrane disposed between the two electrodes.
A fuel cell generates electricity by bringing a fuel gas (typically hydrogen) and an oxidant gas (typically oxygen) respectively to the anode and the cathode. In reaction, a fuel such as hydrogen is oxidized at the anode to form cations (protons) and electrons. The proton exchange membrane facilitates the migration of protons from the anode to the cathode while preventing the electrons from passing through the membrane. As a result, the electrons are forced to flow through an external circuit thus providing an electrical current. At the cathode, oxygen reacts with electrons returned from the electrical circuit to form anions. The anions formed at the cathode react with the protons that have crossed the membrane to form liquid water.
In contrast, an electrolyzer uses electricity to electrolyze water to generate oxygen from its anode and hydrogen from its cathode. Similar to a fuel cell, a typical solid polymer water electrolyzer (SPWE) or proton exchange membrane (PEM) electrolyzer is also comprised of an anode, a cathode and a proton exchange membrane disposed between the two electrodes. Water is introduced to, for example, the anode of the electrolyzer which in turn is connected to the positive pole of a suitable direct current voltage. Oxygen is produced at the anode. The protons then migrate from the anode to the cathode through the membrane. On the cathode which is connected to the negative pole of the direct current voltage, the protons conducted through the membrane are reduced to hydrogen.
In practice, the cells are not operated as single units. Rather, the cells are connected in series, either stacked one on top of the other or placed side by side. The series of cells, referred to as a cell stack, is normally enclosed in a housing. For a fuel cell stack, the fuel and oxidant are directed through manifolds in the housing to the electrodes. The fuel cell is cooled by either the reactants or a cooling medium. The fuel cell stack also comprises current collectors, cell-to-cell seals and insulation while the required piping and instrumentation are provided external to the fuel cell stack. The fuel cell stack, housing and associated hardware constitute a fuel cell module. Likewise, electrolyzer cells are also typically connected in series to form an electrolyzer stack.
A common problem that has to be addressed, for both fuel cell stacks and electrolyzer stacks, is the regulation of water content in the process gas streams. The presence of water in process gas streams typically reduces the efficiency of the electrochemical cell. However, for certain applications, it is advantageous to retain some water content in the gas stream.
There are a variety of devices for exchanging energy and/or mass between at least two fluid streams. Examples of such devices include for example, humidifiers and enthalpy wheels.
Such devices commonly humidify a first gas or fluid stream by transferring humidity from a second fluid stream, also typically containing a gas. In this process, humidity and/or heat from the second fluid stream having higher temperature and higher humidity is retained in the humidifier. The first gas/fluid stream, often having relatively lower humidity and lower temperature flows through the humidifier and picks up the heat and humidity retained therein. In this way, the second gas stream is humidified and heated. This completes the exchange of heat and/or energy between the two streams.
From time to time, liquid water is formed when the second fluid stream loses humidity and heat. The liquid water in the second fluid stream may remain in the second fluid stream, or the liquid water may be retained in the humidifier and picked up by the first fluid stream. In either case, liquid water in the fluid stream may be undesirable.
The inventors have accordingly recognized a need for a fluid separation device for separating liquid from a fluid stream, and adapted for use with humidifiers.